To have a microwave filter satisfying the electrical specifications in terms of insertion loss within the pass band filter and of rejection of undesired signals outside the pass band, it is necessary that each cavity be carefully tuned and that the intensity of the coupling between different cavity be sufficient but not exceeding a well defined limit.
Usually regulating means are introduced for each resonator and between any contiguous cavity: tuning properly these means, typically in the form of screws that pass through the lid and stick inside the body filter for a proper quote, makes the desired frequency response possible to be obtained.
It is known from experience that the manual tuning process is time consuming and quite expensive. It is also known that a filter could be tuned in different frequency bands by simply changing synchronously the resonant frequency of each cavity, maintaining the same coupling strength.
It follows that getting a selective filter tuned in translated bands with the same electric response is possible by simply changing synchronously each cavity's natural frequency.
From an industrial point of view, this technology is needed both for having a flexible design capable of being tuned on customer demand and for the cost reduction related to the manual tuning process.
Moreover, these devices can be remotely tuned even when already deployed on the field, by means of electronically controlled stepper motors.